The present invention is related to container caps generally, and more specifically to container caps having outer shells and methods of making the same.
FIG. 1A is an exploded perspective view of a prior art cosmetic container assembly 10. FIG. 1B is a cross sectional view of the cap portions 110, 120 of the prior art cosmetic container assembly 10. Cosmetic container assemblies, such as are popular for nail polishes, typically include a container 140 and brush 130. The brush 130 is typically secured to a cap 120 through an interference fit between walls 124a, 124b of the cap 120. FIG. 1C is a bottom plan view of cap 120 viewed along lines 3xe2x80x943 of FIG. 1A and depicting walls 124a, 124b. FIG. 1D is a top plan view of brush 130. Alternatively, wall 124a may be absent from the interior of cap 120 and a brush may be sized to fit against the inner surface of wall 124b. Threads 126, which may be formed during molding and facilitate removal of a mold, may help to further secure brush 130. The container 140 is secured to cap 120 through complimentary threads 142a, 142b. 
A cosmetic shell 110 is often placed over a cap 120. It is desirable that the cosmetic shell be aesthetically pleasing in order to promote the cosmetic product. For example, it is generally preferred that the shell have a glossy or shiny appearance. This appearance may be achieved by fitting a gold or silver colored metal shell over a cap. This shell may be as thin as twenty thousandths of an inch. When a metal shell is fitted over a cap 120, the cap 120 does not include threads 122a, and the metal shell is typically glued to the cap 120.
This prior art metal shell configuration suffers from several problems. First, metal shells are expensive to produce. Second, assembling this metal shell configuration requires a gluing stage, thereby adding additional costs to the assembly process as well as additional assembly time.
In order to avoid the problems associated with the metal shell configuration, cosmetic shells 110 have been introduced which are formed from a glossy or shiny plastic. The shells 110 and cap 120 include cooperable threads 122a, 122b for securing the cap 120 to the shell 110. Alternatively, the shell 110 may include a continuous ridge or series of lugs which extend from its inner surface and allow the cap 120 to snap-fit to the shell 110. There are also problems associated with this plastic shell configuration.
First, the threads 122b, ridges, or lugs disposed on the inner surface of the shell 110 are visible on the outer surface of the shell 110 as distortions due to sunken-in areas (xe2x80x9csinksxe2x80x9d) that occur on the surface of the thin plastic shell. It is believed that the sinks form because of differences in solidification rates, i.e., regions of the shell with larger cross sectional thicknesses (e.g., thread regions) shrink more than areas with thinner cross sectional thicknesses (e.g., groove regions) when cooled within a mold. These sinks distort the appearance of the outer shell, particularly when the shell is held at an oblique angle relative to a light source. It is generally recommended that to avoid visible sinks, the distance an internal feature, such as a thread or a lug, extends from a molded wall should not be greater than a third, and more preferably, not more than a quarter, of the thickness of the wall from which it protrudes. Thus, the sinks are not visible if the wall of the shell of a plastic container cap assembly is made sufficiently thick. This additional thickness, however, detracts from the overall aesthetic appearance of the container cap assembly by increasing the overall size of the cap assembly and departing even further from the desired thin metal shell appearance.
The need for cooperable threads 122a, 122b may be avoided by gluing a shell 110 to the cap 120. However, the gluing process introduces additional problems, as discussed above. Therefore, there is presently a need for a more cost effective, but still aesthetically pleasing, cosmetic container cap.
The present invention provides a container cap assembly and method of making the same. A container cap assembly according to the present invention includes a molded plastic base cap including a wall having an inner surface for mating with a container and an outer surface. The outer surface includes a plurality of substantially parallel vertical ribs disposed on the outer surface. The container cap assembly also includes a molded plastic shell sized to surround the outer surface of the base cap. The shell includes a wall having an inner surface and an outer surface. The wall includes a plurality of substantially parallel vertical ribs disposed on the inner surface. The ribs of the shell are disposed to mate with the ribs of the base cap. The ribs of at least one of the base cap and the shell include a plurality of protruded portions extending from the ribs. The shell is fitted over the base cap such that the ribs of the shell frictionally mate with the ribs of the base cap to substantially reduce relative torsional movement between the shell and base cap during the removal of the cap from the container. The protruded portions also deform, either plastically or elastically, when the shell is fitted over the outer surface of the base cap such that the shell is secured to the base cap through an interference fit.
The present invention also provides for another container cap assembly having a molded plastic base cap and molded plastic shell cap. The molded plastic base cap includes a wall having an inner surface for mating with a container and an outer surface. The molded plastic shell cap is sized to surround the outer surface of the base cap and the shell includes a wall having an inner surface and an outer surface. The wall of the base cap or the wall of shell include a plurality of substantially parallel horizontal ribs disposed on the inner surface of the wall of the shell or the outer surface of the wall of the base cap. The ribs include a plurality of protruded portions extending from the ribs such that the protruded portions deform when the shell is fitted over the outer surface of the base cap to secure the base cap and shell cap through an interference fit.
The present invention provides the benefit of cost effective manufacturing with improved aesthetic appearance. The above and other features of the present invention will be better understood from the following detailed description of the preferred embodiments of the invention which is provided in connection with the accompanying drawings.